A View of the Visual Pathway

Tuesday, February 1, 2011

The swift current of visual information flows through the optic nerve from the eye and eventually meets the optic nerve from the other eye. At this point some crossing-over of nerve fibres occurs. Then the nerve enters the brain from either side of the brain stem, connecting with the relay in the lateral geniculate body. From here, optic radiations carry the impulse to the occipital cortex.

For a long time it was thought that the occipital cortex is the final site of visual perception. Then in 1970, the two landmark experiments of (i) Hubel and wiesel and (ii) Horace Barlow and his colleagues, the results of which definitely imply that not even in the occipital cortex is the information gathered and formed into anything like a picture. A large gap still exists in accounting for the conscious perception of visual events.

The visual pathway (and similarly the other pathways as well) has now been traced further into the reticular activating systems by recording secondary evoke potentials. Here the impulse enters a nonspecific system (called a Descending Reticular Activating System) as it descends towards the central region of the brain.